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-rw-r--r--tvix/eval/src/builtins/mod.rs20
-rw-r--r--tvix/eval/src/compiler/mod.rs17
-rw-r--r--tvix/eval/src/errors.rs8
-rw-r--r--tvix/eval/src/eval.rs11
-rw-r--r--tvix/eval/src/value/attrs.rs14
-rw-r--r--tvix/eval/src/value/builtin.rs6
-rw-r--r--tvix/eval/src/value/mod.rs73
-rw-r--r--tvix/eval/src/value/thunk.rs10
-rw-r--r--tvix/eval/src/vm.rs131
9 files changed, 149 insertions, 141 deletions
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index 3c32129e0537..3e1f49d6995a 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -20,12 +20,12 @@ fn pure_builtins() -> Vec<Builtin> {
         Builtin::new("add", 2, |mut args| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
-            Ok(arithmetic_op!(a, b, +))
+            arithmetic_op!(a, b, +)
         }),
         Builtin::new("abort", 1, |mut args| {
-            return Err(
-                ErrorKind::Abort(args.pop().unwrap().to_string()?.as_str().to_owned()).into(),
-            );
+            return Err(ErrorKind::Abort(
+                args.pop().unwrap().to_string()?.as_str().to_owned(),
+            ));
         }),
         Builtin::new("catAttrs", 2, |mut args| {
             let list = args.pop().unwrap().to_list()?;
@@ -43,7 +43,7 @@ fn pure_builtins() -> Vec<Builtin> {
         Builtin::new("div", 2, |mut args| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
-            Ok(arithmetic_op!(a, b, /))
+            arithmetic_op!(a, b, /)
         }),
         Builtin::new("length", 1, |args| {
             Ok(Value::Integer(args[0].as_list()?.len() as i64))
@@ -81,17 +81,17 @@ fn pure_builtins() -> Vec<Builtin> {
         Builtin::new("mul", 2, |mut args| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
-            Ok(arithmetic_op!(a, b, *))
+            arithmetic_op!(a, b, *)
         }),
         Builtin::new("sub", 2, |mut args| {
             let b = args.pop().unwrap();
             let a = args.pop().unwrap();
-            Ok(arithmetic_op!(a, b, -))
+            arithmetic_op!(a, b, -)
         }),
         Builtin::new("throw", 1, |mut args| {
-            return Err(
-                ErrorKind::Throw(args.pop().unwrap().to_string()?.as_str().to_owned()).into(),
-            );
+            return Err(ErrorKind::Throw(
+                args.pop().unwrap().to_string()?.as_str().to_owned(),
+            ));
         }),
         Builtin::new("toString", 1, |args| {
             // TODO: toString is actually not the same as Display
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index d2b08a6b105c..cc98c2e852f2 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -1217,10 +1217,7 @@ impl Compiler<'_> {
     }
 
     fn emit_error(&mut self, span: codemap::Span, kind: ErrorKind) {
-        self.errors.push(Error {
-            kind,
-            span: Some(span),
-        })
+        self.errors.push(Error { kind, span })
     }
 
     /// Convert a non-dynamic string expression to a string if possible,
@@ -1234,7 +1231,7 @@ impl Compiler<'_> {
 
         return Err(Error {
             kind: ErrorKind::DynamicKeyInLet(expr.syntax().clone()),
-            span: Some(self.span_for(&expr)),
+            span: self.span_for(&expr),
         });
     }
 
@@ -1253,7 +1250,7 @@ impl Compiler<'_> {
                 ast::Expr::Str(s) => self.expr_str_to_string(s),
                 _ => Err(Error {
                     kind: ErrorKind::DynamicKeyInLet(node.syntax().clone()),
-                    span: Some(self.span_for(&node)),
+                    span: self.span_for(&node),
                 }),
             },
         }
@@ -1319,8 +1316,12 @@ pub fn compile<'code>(
 ) -> EvalResult<CompilationOutput> {
     let mut root_dir = match location {
         Some(dir) => Ok(dir),
-        None => std::env::current_dir().map_err(|e| {
-            ErrorKind::PathResolution(format!("could not determine current directory: {}", e))
+        None => std::env::current_dir().map_err(|e| Error {
+            kind: ErrorKind::PathResolution(format!(
+                "could not determine current directory: {}",
+                e
+            )),
+            span: file.span,
         }),
     }?;
 
diff --git a/tvix/eval/src/errors.rs b/tvix/eval/src/errors.rs
index aced6f6a5571..59142f2efe64 100644
--- a/tvix/eval/src/errors.rs
+++ b/tvix/eval/src/errors.rs
@@ -53,13 +53,7 @@ pub enum ErrorKind {
 #[derive(Clone, Debug)]
 pub struct Error {
     pub kind: ErrorKind,
-    pub span: Option<codemap::Span>,
-}
-
-impl From<ErrorKind> for Error {
-    fn from(kind: ErrorKind) -> Self {
-        Error { span: None, kind }
-    }
+    pub span: codemap::Span,
 }
 
 impl Display for Error {
diff --git a/tvix/eval/src/eval.rs b/tvix/eval/src/eval.rs
index c72e40c75d34..1362c0394d27 100644
--- a/tvix/eval/src/eval.rs
+++ b/tvix/eval/src/eval.rs
@@ -2,7 +2,7 @@ use std::path::PathBuf;
 
 use crate::{
     builtins::global_builtins,
-    errors::{ErrorKind, EvalResult},
+    errors::{Error, ErrorKind, EvalResult},
     value::Value,
 };
 
@@ -23,7 +23,10 @@ pub fn interpret(code: &str, location: Option<PathBuf>) -> EvalResult<Value> {
         for err in errors {
             eprintln!("parse error: {}", err);
         }
-        return Err(ErrorKind::ParseErrors(errors.to_vec()).into());
+        return Err(Error {
+            kind: ErrorKind::ParseErrors(errors.to_vec()).into(),
+            span: file.span,
+        });
     }
 
     // If we've reached this point, there are no errors.
@@ -54,8 +57,8 @@ pub fn interpret(code: &str, location: Option<PathBuf>) -> EvalResult<Value> {
         eprintln!(
             "compiler error: {:?} at `{}`[line {}]",
             error.kind,
-            file.source_slice(error.span.expect("TODO: non-optional")),
-            file.find_line(error.span.unwrap().low()) + 1
+            file.source_slice(error.span),
+            file.find_line(error.span.low()) + 1
         );
     }
 
diff --git a/tvix/eval/src/value/attrs.rs b/tvix/eval/src/value/attrs.rs
index 2954f8522097..d122f9155d2c 100644
--- a/tvix/eval/src/value/attrs.rs
+++ b/tvix/eval/src/value/attrs.rs
@@ -10,7 +10,7 @@ use std::collections::BTreeMap;
 use std::fmt::Display;
 use std::rc::Rc;
 
-use crate::errors::{ErrorKind, EvalResult};
+use crate::errors::ErrorKind;
 
 use super::string::NixString;
 use super::Value;
@@ -236,7 +236,7 @@ impl NixAttrs {
 
     /// Implement construction logic of an attribute set, to encapsulate
     /// logic about attribute set optimisations inside of this module.
-    pub fn construct(count: usize, mut stack_slice: Vec<Value>) -> EvalResult<Self> {
+    pub fn construct(count: usize, mut stack_slice: Vec<Value>) -> Result<Self, ErrorKind> {
         debug_assert!(
             stack_slice.len() == count * 2,
             "construct_attrs called with count == {}, but slice.len() == {}",
@@ -342,12 +342,11 @@ fn attempt_optimise_kv(slice: &mut [Value]) -> Option<NixAttrs> {
 
 // Set an attribute on an in-construction attribute set, while
 // checking against duplicate keys.
-fn set_attr(attrs: &mut NixAttrs, key: NixString, value: Value) -> EvalResult<()> {
+fn set_attr(attrs: &mut NixAttrs, key: NixString, value: Value) -> Result<(), ErrorKind> {
     match attrs.0.map_mut().entry(key) {
         btree_map::Entry::Occupied(entry) => Err(ErrorKind::DuplicateAttrsKey {
             key: entry.key().as_str().to_string(),
-        }
-        .into()),
+        }),
 
         btree_map::Entry::Vacant(entry) => {
             entry.insert(value);
@@ -367,7 +366,7 @@ fn set_nested_attr(
     key: NixString,
     mut path: Vec<NixString>,
     value: Value,
-) -> EvalResult<()> {
+) -> Result<(), ErrorKind> {
     // If there is no next key we are at the point where we
     // should insert the value itself.
     if path.is_empty() {
@@ -408,8 +407,7 @@ fn set_nested_attr(
             _ => {
                 return Err(ErrorKind::DuplicateAttrsKey {
                     key: entry.key().as_str().to_string(),
-                }
-                .into())
+                })
             }
         },
     }
diff --git a/tvix/eval/src/value/builtin.rs b/tvix/eval/src/value/builtin.rs
index e876c235557e..d1248b1ec219 100644
--- a/tvix/eval/src/value/builtin.rs
+++ b/tvix/eval/src/value/builtin.rs
@@ -3,13 +3,13 @@
 //!
 //! Builtins are directly backed by Rust code operating on Nix values.
 
-use crate::errors::EvalResult;
+use crate::errors::ErrorKind;
 
 use super::Value;
 
 use std::fmt::{Debug, Display};
 
-pub type BuiltinFn = fn(arg: Vec<Value>) -> EvalResult<Value>;
+pub type BuiltinFn = fn(arg: Vec<Value>) -> Result<Value, ErrorKind>;
 
 /// Represents a single built-in function which directly executes Rust
 /// code that operates on a Nix value.
@@ -50,7 +50,7 @@ impl Builtin {
     /// Apply an additional argument to the builtin, which will either
     /// lead to execution of the function or to returning a partial
     /// builtin.
-    pub fn apply(mut self, arg: Value) -> EvalResult<Value> {
+    pub fn apply(mut self, arg: Value) -> Result<Value, ErrorKind> {
         self.partials.push(arg);
 
         if self.partials.len() == self.arity {
diff --git a/tvix/eval/src/value/mod.rs b/tvix/eval/src/value/mod.rs
index a8bfc164cdf9..5cfad2e66ea8 100644
--- a/tvix/eval/src/value/mod.rs
+++ b/tvix/eval/src/value/mod.rs
@@ -10,7 +10,7 @@ mod list;
 mod string;
 mod thunk;
 
-use crate::errors::{ErrorKind, EvalResult};
+use crate::errors::ErrorKind;
 use crate::opcode::StackIdx;
 pub use attrs::NixAttrs;
 pub use builtin::Builtin;
@@ -70,91 +70,59 @@ impl Value {
         }
     }
 
-    pub fn as_bool(&self) -> EvalResult<bool> {
+    pub fn as_bool(&self) -> Result<bool, ErrorKind> {
         match self {
             Value::Bool(b) => Ok(*b),
-            other => Err(ErrorKind::TypeError {
-                expected: "bool",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("bool", &other)),
         }
     }
 
-    pub fn as_attrs(&self) -> EvalResult<&NixAttrs> {
+    pub fn as_attrs(&self) -> Result<&NixAttrs, ErrorKind> {
         match self {
             Value::Attrs(attrs) => Ok(attrs),
-            other => Err(ErrorKind::TypeError {
-                expected: "set",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("set", &other)),
         }
     }
 
-    pub fn as_str(&self) -> EvalResult<&str> {
+    pub fn as_str(&self) -> Result<&str, ErrorKind> {
         match self {
             Value::String(s) => Ok(s.as_str()),
-            other => Err(ErrorKind::TypeError {
-                expected: "string",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("string", &other)),
         }
     }
 
-    pub fn as_list(&self) -> EvalResult<&NixList> {
+    pub fn as_list(&self) -> Result<&NixList, ErrorKind> {
         match self {
             Value::List(xs) => Ok(xs),
-            other => Err(ErrorKind::TypeError {
-                expected: "list",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("list", &other)),
         }
     }
 
-    pub fn to_string(self) -> EvalResult<NixString> {
+    pub fn to_string(self) -> Result<NixString, ErrorKind> {
         match self {
             Value::String(s) => Ok(s),
-            other => Err(ErrorKind::TypeError {
-                expected: "string",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("string", &other)),
         }
     }
 
-    pub fn to_attrs(self) -> EvalResult<Rc<NixAttrs>> {
+    pub fn to_attrs(self) -> Result<Rc<NixAttrs>, ErrorKind> {
         match self {
             Value::Attrs(s) => Ok(s),
-            other => Err(ErrorKind::TypeError {
-                expected: "set",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("set", &other)),
         }
     }
 
-    pub fn to_list(self) -> EvalResult<NixList> {
+    pub fn to_list(self) -> Result<NixList, ErrorKind> {
         match self {
             Value::List(l) => Ok(l),
-            other => Err(ErrorKind::TypeError {
-                expected: "list",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("list", &other)),
         }
     }
 
-    pub fn to_closure(self) -> EvalResult<Closure> {
+    pub fn to_closure(self) -> Result<Closure, ErrorKind> {
         match self {
             Value::Closure(c) => Ok(c),
-            other => Err(ErrorKind::TypeError {
-                expected: "lambda",
-                actual: other.type_of(),
-            }
-            .into()),
+            other => Err(type_error("lambda", &other)),
         }
     }
 
@@ -231,3 +199,10 @@ impl PartialEq for Value {
         }
     }
 }
+
+fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
+    ErrorKind::TypeError {
+        expected,
+        actual: actual.type_of(),
+    }
+}
diff --git a/tvix/eval/src/value/thunk.rs b/tvix/eval/src/value/thunk.rs
index 307eb23a75f6..c2552284fe20 100644
--- a/tvix/eval/src/value/thunk.rs
+++ b/tvix/eval/src/value/thunk.rs
@@ -24,7 +24,7 @@ use std::{
     rc::Rc,
 };
 
-use crate::{errors::ErrorKind, upvalues::UpvalueCarrier, vm::VM, EvalResult, Value};
+use crate::{errors::ErrorKind, upvalues::UpvalueCarrier, vm::VM, Value};
 
 use super::Lambda;
 
@@ -64,7 +64,7 @@ impl Thunk {
     /// to it, providing memoization) through interior mutability. In
     /// case of nested thunks, the intermediate thunk representations
     /// are replaced.
-    pub fn force(&self, vm: &mut VM) -> EvalResult<()> {
+    pub fn force(&self, vm: &mut VM) -> Result<(), ErrorKind> {
         // Due to mutable borrowing rules, the following code can't
         // easily use a match statement or something like that; it
         // requires a bit of manual fiddling.
@@ -78,14 +78,16 @@ impl Thunk {
                 }
 
                 ThunkRepr::Evaluated(_) => return Ok(()),
-                ThunkRepr::Blackhole => return Err(ErrorKind::InfiniteRecursion.into()),
+                ThunkRepr::Blackhole => return Err(ErrorKind::InfiniteRecursion),
 
                 ThunkRepr::Suspended { .. } => {
                     if let ThunkRepr::Suspended { lambda, upvalues } =
                         std::mem::replace(&mut *thunk_mut, ThunkRepr::Blackhole)
                     {
                         vm.call(lambda, upvalues, 0);
-                        *thunk_mut = ThunkRepr::Evaluated(vm.run()?);
+                        // TODO: find a cheap way to actually retain
+                        // the original error span
+                        *thunk_mut = ThunkRepr::Evaluated(vm.run().map_err(|e| e.kind)?);
                     }
                 }
             }
diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index a2b370ab9288..5fabdb491e1f 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -6,7 +6,7 @@ use std::{cell::RefMut, rc::Rc};
 use crate::{
     chunk::Chunk,
     errors::{Error, ErrorKind, EvalResult},
-    opcode::{ConstantIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx},
+    opcode::{CodeIdx, ConstantIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx},
     upvalues::UpvalueCarrier,
     value::{Closure, Lambda, NixAttrs, NixList, Thunk, Value},
 };
@@ -37,30 +37,50 @@ pub struct VM {
     with_stack: Vec<usize>,
 }
 
+/// This macro wraps a computation that returns an ErrorKind or a
+/// result, and wraps the ErrorKind in an Error struct if present.
+///
+/// The reason for this macro's existence is that calculating spans is
+/// potentially expensive, so it should be avoided to the last moment
+/// (i.e. definite instantiation of a runtime error) if possible.
+macro_rules! fallible {
+    ( $self:ident, $body:expr) => {
+        match $body {
+            Ok(result) => result,
+            Err(kind) => {
+                return Err(Error {
+                    kind,
+                    span: $self.current_span(),
+                })
+            }
+        }
+    };
+}
+
 #[macro_export]
 macro_rules! arithmetic_op {
     ( $self:ident, $op:tt ) => {{
         let b = $self.pop();
         let a = $self.pop();
-        let result = arithmetic_op!(a, b, $op);
+        let result = fallible!($self, arithmetic_op!(a, b, $op));
         $self.push(result);
     }};
 
     ( $a:ident, $b:ident, $op:tt ) => {{
         match ($a, $b) {
-            (Value::Integer(i1), Value::Integer(i2)) => Value::Integer(i1 $op i2),
-            (Value::Float(f1), Value::Float(f2)) => Value::Float(f1 $op f2),
-            (Value::Integer(i1), Value::Float(f2)) => Value::Float(i1 as f64 $op f2),
-            (Value::Float(f1), Value::Integer(i2)) => Value::Float(f1 $op i2 as f64),
+            (Value::Integer(i1), Value::Integer(i2)) => Ok(Value::Integer(i1 $op i2)),
+            (Value::Float(f1), Value::Float(f2)) => Ok(Value::Float(f1 $op f2)),
+            (Value::Integer(i1), Value::Float(f2)) => Ok(Value::Float(i1 as f64 $op f2)),
+            (Value::Float(f1), Value::Integer(i2)) => Ok(Value::Float(f1 $op i2 as f64)),
 
-            (v1, v2) => return Err(ErrorKind::TypeError {
+            (v1, v2) => Err(ErrorKind::TypeError {
                 expected: "number (either int or float)",
                 actual: if v1.is_number() {
                     v2.type_of()
                 } else {
                     v1.type_of()
                 },
-            }.into()),
+            }),
         }
     }};
 }
@@ -80,10 +100,10 @@ macro_rules! cmp_op {
             (Value::Float(f1), Value::Integer(i2)) => f1 $op (i2 as f64),
             (Value::String(s1), Value::String(s2)) => s1 $op s2,
 
-            (lhs, rhs) => return Err(ErrorKind::Incomparable {
+            (lhs, rhs) => return Err($self.error(ErrorKind::Incomparable {
                 lhs: lhs.type_of(),
                 rhs: rhs.type_of(),
-            }.into()),
+            })),
         };
 
         $self.push(Value::Bool(result));
@@ -126,6 +146,21 @@ impl VM {
         &self.stack[self.stack.len() - 1 - offset]
     }
 
+    /// Returns the source span of the instruction currently being
+    /// executed.
+    fn current_span(&self) -> codemap::Span {
+        self.chunk().get_span(CodeIdx(self.frame().ip - 1))
+    }
+
+    /// Construct an error from the given ErrorKind and the source
+    /// span of the current instruction.
+    fn error(&self, kind: ErrorKind) -> Error {
+        Error {
+            kind,
+            span: self.current_span(),
+        }
+    }
+
     pub fn call(&mut self, lambda: Rc<Lambda>, upvalues: Vec<Value>, arg_count: usize) {
         let frame = CallFrame {
             lambda,
@@ -171,7 +206,7 @@ impl VM {
                     let result = if let (Value::String(s1), Value::String(s2)) = (&a, &b) {
                         Value::String(s1.concat(s2))
                     } else {
-                        arithmetic_op!(a, b, +)
+                        fallible!(self, arithmetic_op!(a, b, +))
                     };
 
                     self.push(result)
@@ -182,7 +217,7 @@ impl VM {
                 OpCode::OpDiv => arithmetic_op!(self, /),
 
                 OpCode::OpInvert => {
-                    let v = self.pop().as_bool()?;
+                    let v = fallible!(self, self.pop().as_bool());
                     self.push(Value::Bool(!v));
                 }
 
@@ -190,11 +225,10 @@ impl VM {
                     Value::Integer(i) => self.push(Value::Integer(-i)),
                     Value::Float(f) => self.push(Value::Float(-f)),
                     v => {
-                        return Err(ErrorKind::TypeError {
+                        return Err(self.error(ErrorKind::TypeError {
                             expected: "number (either int or float)",
                             actual: v.type_of(),
-                        }
-                        .into())
+                        }));
                     }
                 },
 
@@ -218,30 +252,29 @@ impl VM {
                 OpCode::OpAttrPath(Count(count)) => self.run_attr_path(count)?,
 
                 OpCode::OpAttrsUpdate => {
-                    let rhs = unwrap_or_clone_rc(self.pop().to_attrs()?);
-                    let lhs = unwrap_or_clone_rc(self.pop().to_attrs()?);
+                    let rhs = unwrap_or_clone_rc(fallible!(self, self.pop().to_attrs()));
+                    let lhs = unwrap_or_clone_rc(fallible!(self, self.pop().to_attrs()));
 
                     self.push(Value::Attrs(Rc::new(lhs.update(rhs))))
                 }
 
                 OpCode::OpAttrsSelect => {
-                    let key = self.pop().to_string()?;
-                    let attrs = self.pop().to_attrs()?;
+                    let key = fallible!(self, self.pop().to_string());
+                    let attrs = fallible!(self, self.pop().to_attrs());
 
                     match attrs.select(key.as_str()) {
                         Some(value) => self.push(value.clone()),
 
                         None => {
-                            return Err(ErrorKind::AttributeNotFound {
+                            return Err(self.error(ErrorKind::AttributeNotFound {
                                 name: key.as_str().to_string(),
-                            }
-                            .into())
+                            }))
                         }
                     }
                 }
 
                 OpCode::OpAttrsTrySelect => {
-                    let key = self.pop().to_string()?;
+                    let key = fallible!(self, self.pop().to_string());
                     let value = match self.pop() {
                         Value::Attrs(attrs) => match attrs.select(key.as_str()) {
                             Some(value) => value.clone(),
@@ -255,7 +288,7 @@ impl VM {
                 }
 
                 OpCode::OpAttrsIsSet => {
-                    let key = self.pop().to_string()?;
+                    let key = fallible!(self, self.pop().to_string());
                     let result = match self.pop() {
                         Value::Attrs(attrs) => attrs.contains(key.as_str()),
 
@@ -274,8 +307,8 @@ impl VM {
                 }
 
                 OpCode::OpConcat => {
-                    let rhs = self.pop().to_list()?;
-                    let lhs = self.pop().to_list()?;
+                    let rhs = fallible!(self, self.pop().to_list());
+                    let lhs = fallible!(self, self.pop().to_list());
                     self.push(Value::List(lhs.concat(&rhs)))
                 }
 
@@ -286,13 +319,13 @@ impl VM {
                 }
 
                 OpCode::OpJumpIfTrue(JumpOffset(offset)) => {
-                    if self.peek(0).as_bool()? {
+                    if fallible!(self, self.peek(0).as_bool()) {
                         self.frame_mut().ip += offset;
                     }
                 }
 
                 OpCode::OpJumpIfFalse(JumpOffset(offset)) => {
-                    if !self.peek(0).as_bool()? {
+                    if !fallible!(self, self.peek(0).as_bool()) {
                         self.frame_mut().ip += offset;
                     }
                 }
@@ -311,11 +344,10 @@ impl VM {
                 OpCode::OpAssertBool => {
                     let val = self.peek(0);
                     if !val.is_bool() {
-                        return Err(ErrorKind::TypeError {
+                        return Err(self.error(ErrorKind::TypeError {
                             expected: "bool",
                             actual: val.type_of(),
-                        }
-                        .into());
+                        }));
                     }
                 }
 
@@ -347,13 +379,13 @@ impl VM {
                 }
 
                 OpCode::OpResolveWith => {
-                    let ident = self.pop().to_string()?;
+                    let ident = fallible!(self, self.pop().to_string());
                     let value = self.resolve_with(ident.as_str())?;
                     self.push(value)
                 }
 
                 OpCode::OpResolveWithOrUpvalue(idx) => {
-                    let ident = self.pop().to_string()?;
+                    let ident = fallible!(self, self.pop().to_string());
                     match self.resolve_with(ident.as_str()) {
                         // Variable found in local `with`-stack.
                         Ok(value) => self.push(value),
@@ -372,8 +404,8 @@ impl VM {
                 }
 
                 OpCode::OpAssert => {
-                    if !self.pop().as_bool()? {
-                        return Err(ErrorKind::AssertionFailed.into());
+                    if !fallible!(self, self.pop().as_bool()) {
+                        return Err(self.error(ErrorKind::AssertionFailed));
                     }
                 }
 
@@ -386,19 +418,18 @@ impl VM {
 
                         Value::Builtin(builtin) => {
                             let arg = self.pop();
-                            let result = builtin.apply(arg)?;
+                            let result = fallible!(self, builtin.apply(arg));
                             self.push(result);
                         }
-                        _ => return Err(ErrorKind::NotCallable.into()),
+                        _ => return Err(self.error(ErrorKind::NotCallable)),
                     };
                 }
 
                 OpCode::OpGetUpvalue(upv_idx) => {
                     let value = self.frame().upvalue(upv_idx).clone();
                     if let Value::DynamicUpvalueMissing(name) = value {
-                        return Err(
-                            ErrorKind::UnknownDynamicVariable(name.as_str().to_string()).into()
-                        );
+                        return Err(self
+                            .error(ErrorKind::UnknownDynamicVariable(name.as_str().to_string())));
                     }
 
                     self.push(value);
@@ -446,7 +477,7 @@ impl VM {
                     let mut value = self.pop();
 
                     if let Value::Thunk(thunk) = value {
-                        thunk.force(self)?;
+                        fallible!(self, thunk.force(self));
                         value = thunk.value().clone();
                     }
 
@@ -498,7 +529,7 @@ impl VM {
         let mut path = Vec::with_capacity(count);
 
         for _ in 0..count {
-            path.push(self.pop().to_string()?);
+            path.push(fallible!(self, self.pop().to_string()));
         }
 
         self.push(Value::AttrPath(path));
@@ -506,7 +537,11 @@ impl VM {
     }
 
     fn run_attrset(&mut self, count: usize) -> EvalResult<()> {
-        let attrs = NixAttrs::construct(count, self.stack.split_off(self.stack.len() - count * 2))?;
+        let attrs = fallible!(
+            self,
+            NixAttrs::construct(count, self.stack.split_off(self.stack.len() - count * 2))
+        );
+
         self.push(Value::Attrs(Rc::new(attrs)));
         Ok(())
     }
@@ -518,7 +553,7 @@ impl VM {
         let mut out = String::new();
 
         for _ in 0..count {
-            out.push_str(self.pop().to_string()?.as_str());
+            out.push_str(fallible!(self, self.pop().to_string()).as_str());
         }
 
         self.push(Value::String(out.into()));
@@ -527,7 +562,7 @@ impl VM {
 
     fn resolve_dynamic_upvalue(&mut self, ident_idx: ConstantIdx) -> EvalResult<Value> {
         let chunk = self.chunk();
-        let ident = chunk.constant(ident_idx).as_str()?.to_string();
+        let ident = fallible!(self, chunk.constant(ident_idx).as_str()).to_string();
 
         // Peek at the current instruction (note: IP has already
         // advanced!) to see if it is actually data indicating a
@@ -560,14 +595,14 @@ impl VM {
     /// Resolve a dynamic identifier through the with-stack at runtime.
     fn resolve_with(&self, ident: &str) -> EvalResult<Value> {
         for idx in self.with_stack.iter().rev() {
-            let with = self.stack[*idx].as_attrs()?;
+            let with = fallible!(self, self.stack[*idx].as_attrs());
             match with.select(ident) {
                 None => continue,
                 Some(val) => return Ok(val.clone()),
             }
         }
 
-        Err(ErrorKind::UnknownDynamicVariable(ident.to_string()).into())
+        Err(self.error(ErrorKind::UnknownDynamicVariable(ident.to_string())))
     }
 
     /// Populate the upvalue fields of a thunk or closure under construction.
@@ -619,7 +654,7 @@ impl VM {
             Value::List(list) => list.iter().try_for_each(|elem| self.force_for_output(elem)),
 
             Value::Thunk(thunk) => {
-                thunk.force(self)?;
+                fallible!(self, thunk.force(self));
                 self.force_for_output(&thunk.value())
             }